Around this time those of us with an astronomer in the family are faced with finding presents that will be useful and appreciated.
Similarly those astronomers should have been dropping helpful hints regarding things he or she really would love to have. However, if the astronomer is too polite to do that, or is a raw beginner, here are a few suggestions for suitable presents.
Every year the choices get more bewildering. There are telescopes with various degrees of automation, the most sophisticated of which just need to be set up, turned on, and then, after a pause, just told what object to point at. However, it is still good to have some understanding of the basics of astronomy. There are lots of things for meeting this need which will make good presents. A backyard astronomerís first present should be a pair of good binoculars. The Moon, star clusters and exploratory trips along the Milky Way are great experiences. Binoculars are also good for searching for and observing comets.
Binoculars are described by a pair of numbers, for example 8×30 or 10×50, where the “x” is pronounced “times,” as in seven times 50. The first figure is the magnification and the second is the diameter of the objective lens in millimetres. The objective lens has the job of collecting the light and forming the image, which is viewed and magnified by the eyepiece lens. Since many astronomical objects appear quite large in the sky but are faint, the size of the objective lens is very important; within limits, bigger is definitely better. Magnification is great, but it does not just make things look bigger, it also makes all the shakiness in your hands look bigger too.
Observing involves looking at things or searching the sky for many minutes at a time, so having to stop because of tired, shaking hands is not fun. A pair of 7×50 binoculars would be a good choice, or for those with strong, steady hands, a pair of 10×50’s. If the astronomer already has a pair of binoculars, a good-quality telescope would be the next step. However, this is a buyer beware topic. The market is filled with complex looking telescopes offering incredible magnifications, such as 300 or even more than 400 times, that are basically worthless. A rule of thumb for spotting junk telescopes is the magnification they offer. A telescope of average quality can be used at magnifications as high as the diameter of the objective lens or mirror in millimetres. If it has an 80mm objective it will be useful for magnifications of up to 80 times. A high-quality telescope will have better lenses and may be pushed to twice that magnification: two times per millimetre of objective lens or mirror diameter. The limits of telescope magnification are set by the fundamental nature of light, not technology.
Even in the age of star map apps, a planisphere is a great idea. These consist of two plastic discs (don’t get cardboard ones). Set the date against the time and the window shows what is in the sky. These have no batteries to go flat, donít make a lot of light and ruin your night vision, and donít mind being dropped in the mud and trodden on. Add a copy of the Observer’s Handbook, produced each year by the Royal Astronomical Society of Canada, and the family astronomer will be well set up for a year of productive observing.
When not an expert, deal with experts. If possible, do your astronomical Christmas shopping at the local science store. See the equipment, discuss whatís wanted; try it out. Binoculars and telescopes should produce sharp, clean images and be easy to use, with no discomfort. If there is no science store available, contact your local astronomy society for advice. It will be worth it.
Venus is low in the southwest after sunset. Look for a bright, starlike object, shining steadily. Mars is low in the Southwest in the evening. Jupiter rises in the early hours. The Moon will be New on the Dec. 29 and will reach First Quarter on the 7th.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.